This invention relates generally to solid-state masers, that is, microwave amplification by stimulated emission of radiation, and more particularly to a maser for generating low-power signals in the submillimeter frequency range.
A number of devices for generating submillimeter radiation has been developed but these mechanisms are incapable of low-power operation. Devices of the electron cyclotron maser type (J. L. Hirschfeld and V. L. Granatstein, IEEE Trans. on Microwave Theo. and Tech., MTT 25, 522 (1977)) are capable of extremely high power output (as high as 10.sup.9 watts), but they are incapable of operating in a low-power mode because the electron beam must be accelerated to relativistic velocities.
For the optically pumped solid state maser technique (B. Lax, "Quantum Electronics", Columbia University Press (New York, 1968), p. 248), optical pumping is used to invert the population of two specific adjacent Landau energy levels in the conduction band of a semiconductor, Carrier relaxation between these levels should give submillimeter radiation. However, attempts to implement this configuration have been unsuccessful because monochromatic sources at the proper wavelength have not been available with sufficient power.
An optically pumped submillimeter laser (Sessions M-3: Proceedings of the 2nd Intl. Conf. and Winter School on submillimeter waves and their applications, Editor S. Perkowitz, Dec. 6-11, 1976, San Juan, Puerto Rico) is a submillimeter wave gas laser which is pumped by a high power CO.sub.2 laser and is a commonly used source for laboratory measurements. However, it is a very bulky and inefficient source. In addition, sources are available only at certain discrete frequencies where known laser lines exist.
Klystron tubes are available at frequencies as high as 1000 GHz. Submillimeter wave signals are obtained by generating harmonics using a mixer. For example, 1000 GHz can be obtained from the 10th harmonic of a 100 GHz signal. Obviously this is a bulky and inefficient signal source in the submillimeter frequency range.
It is desirable to efficiently generate signals in the submillimeter frequency range for use, for example, as a local oscillator in radar and communications receivers, or as a source for laboratory measurements.